1. Field of Use
This invention relates generally to improved register control means for web processing apparatus.
2. Description of the Prior Art
Many products, such as frozen foods and canned or bottled drinks, are marketed in cartons on which graphics are printed. Such cartons are formed by folding pre-printed blanks which are cut from a paperboard web. The blanks are formed by running a continuous paperboard web through web processing apparatus which typically comprises a multicolor gravure type printing press and a cutter-creaser press located downstream of the printing press. The printing press comprises a series of printing stations, one for each color, which cooperate to form a succession of multicolor printed impressions and associated register marks on the web. Each printing station comprises a rotary impression cylinder which has a certain circumference or repeat length which, for example, typically ranges from 17" to 40", depending on the size selected for a specific press run. The cutter-creaser press, which is marketed as a separate machine for use with printing presses having impression cylinders of various circumferences (repeat lengths), is designed and constructed to take this fact into account.
As FIG. 13 shows, one prior art cutter-creaser press manufactured and sold by the same assignee as the present invention (designated as Model VP3000) comprises a reciprocating cutter-creaser mechanism having a cutting zone wherein cutter blades and creaser blades are located to cut pre-printed foldable blanks from the web. The cutter-creaser press further comprises a pair of continuously rotating metering rolls, one being a motor-driven metering roll, defining a nip which engages the preprinted web and feeds it from the impression cylinder in the last printing station to the cutter-creaser mechanism. The cutter-creaser press further comprises components which ensure that the impressions on the web properly register with the cutting zone in the cutter-creaser mechanism. Such components include a movable dancer located between the impression cylinder and the metering rolls to maintain tension on the web. A movable curve plate and a pair of intermittently operable cutter feed rolls are located between the metering rolls and the cutter-creaser mechanism. In operation, the cutter-creaser mechanism moves reciprocably between open (infeed) and closed (cutting) positions. When the cutter-creaser mechanism is open, the cutter feed rolls close and feed a length of web into the cutting zone. When the cutter creaser mechanism is closed, the cutter feed rolls open to momentarily stop web feed into the cutting zone and the movable curve plate moves to take up the slack in the web which is being continuously fed by the metering rolls.
Generally speaking, proper registration of the blades in the cutting zone and a printed impression on the web is obtained by matching the surface speed [feed-up]of the metering rolls to a specific printed mark applied by the impression cylinder in any previous printing station. Print-to-cut register error is a direct function of the preciseness of this surface speed or feed-up.
The reciprocating cutter-creaser mechanism is driven by a main drive motor. However, as previously mentioned, the circumference (repeat length) of the last impression cylinder can vary between 17" and 40", depending on job requirements, whereas the metering roll circumference has a fixed predetermined circumference. Therefore, the cutter-creaser mechanism is provided with a variable ratio power transmission unit which is connected between the main drive motor and both the cutter-creaser mechanism and the metering rolls to obtain the required surface speed match.
The variable ratio power transmission unit comprises a set of change gears and a variable ratio planetary differential.
A set of change gears of appropriate size is selected and manually installed so as to adjust the speed of the metering rolls within a 2% increment of the desired repeat length which is to be produced.
The planetary differential is used as an infinitely variable ratio device to further adjust the speed of the metering rolls to any value within the 2% increment range provided by the change gears. The ratio of the planetary differential is adjusted by rotating the cage of the planetary differential using a high response, low armature inertia, DC servo motor, hereinafter referred to as a register control motor. The register control motor is connected to the cage of the planetary differential using an integral 60:1 ratio worm gear drive, for example, to prevent tension feedback from the running web.
The prior art register control means shown in FIG. 13 for the aforedescribed Model VP3000 cutter-creaser press includes the following electrical devices, namely: a dancer position sensor, a register mark scanner located just ahead of the metering rolls, a metering roll encoder, a motor control unit for the register control motor and a cut-stroke signal generator.
The prior art register control means further includes electric control circuits for receiving electric output signals from the aforesaid electrical devices and for providing electric output signals to the motor control unit to effect registration.
The operator's control unit for the prior art register control is shown in FIG. 14 and employs five visual display devices, including an oscilloscope, which need to be monitored by the operator, numerous manually controlled switches and two manually controlled potentiometers P1 and P2 which need to be manually adjusted during set-up and running to effect registration. One potentiometer P2 sets the base speed of the register control motor during set-up. The other potentiometer P1 operates to adjust the position of the dancer during set-up to ensure proper registration. In the prior art system, it was necessary for the operator to frequently adjust potentiometers P1 and P2 when restarting the system after a shutdown to maintain registration.